NovaSandler
Noah Sandler is a Magic Online veteran originally known for founding ModoSharks.com. He's been infinite from drafting for over a decade, won 36 consecutive matches in Odyssey Block flashbacks, and has eclipsed 2000 Limited rating on MTGO twice. He streams on Twitch as modogrinder1 and offers draft coaching via Skype.

MtGNotifier
Can trigger a sound effect when receiving trade requests or messages, and includes hundreds of MtG Symbols for chat and the classifieds. Free to download.

Magic Online Playmats and Other Resources for Limited
This page contains freely downloadable resources, including Magic Online playmats and Magic Online-compatible lists, to help remind you what spells your opponent could cast during your turn with his or her available mana.